Arthur Fischer
Reputation
37,690
99/100 score
5 38 83
Impact
~289k people reached

# 4,361 Actions

 6h revised $\operatorname{Fr}( p(\overline U) )$ where $p : X \to Y$ is a closed, not necessarily continuous, surjection, and $U \subset X$ is open added 40 characters in body; edited tags; edited title 20h revised Given n girls and boys how many ways are there to arrange them such that any two boys have atleast 'k' girls between them. example appears to be for K=3 (at least K girls between any two boys) 23h revised Krull's height theorem in the non-Noetherian case added 69 characters in body; edited tags; edited title 1d revised Proving $\neg ( \neg \alpha \wedge \neg \neg \alpha )$ deleted 136 characters in body 1d comment Vector spaces whose elements are functions Comments are not for extended discussion; this conversation has been moved to chat. 2d revised Dirichlet integral using real Analysis appended answer 1250840 as supplemental 2d answered $X$ is A-space iff the frontier of any closed set in $X$ is compact. 2d comment Pos of Matrix is a closed set? @H.Reza If that's what you want to do just fill out the form here. 2d comment Pos of Matrix is a closed set? @H.Reza It is quite bad form to simply delete a closed question, and then re-ask it without any changes. If you continue to do this very bad things may happen. (Please read that last part in an ominous voice, as intended.) 2d comment If the sum of $n$ terms of an A.P. is $2n+3n^2$, find the $r^{th}$ term. The original Solutions of the Examples in Higher Algebra is available from the Internet Archive in a variety of formats. See here. Apr24 comment Finding minimum value of a trigonometric expression That the exact same answer provides a solution to two different questions is an indication that one should probably be closed as a duplicate of the other. Apr24 revised $X$ is A-space iff the frontier of any closed set in $X$ is compact. added 45 characters in body; edited tags Apr23 revised Verifying $(A \bigtriangleup B) \cup C=(A \cup C) \bigtriangleup (B\setminus C)$ added 3 characters in body; edited tags; edited title Apr23 revised Is there a metric proof for the Caristi theorem? fixed formatting Apr22 revised Closure, interior, boundary and exterior of $A = (-\infty, 1) \cup [2, \infty)$ as a subset of $\mathbb R$ with the half open line topology Sorgenfrey Apr22 revised Closure, interior, boundary and exterior of $A = (-\infty, 1) \cup [2, \infty)$ as a subset of $\mathbb R$ with the half open line topology added 52 characters in body; edited tags; edited title Apr22 revised Compute $f(2)$ if $\int_0^{x^2(1+x)} f(t) dt = x$ for all $x \geq 0$ added 9 characters in body; edited title Apr22 revised Compute $f(2)$ if $\int_0^{x^2(1+x)} f(t) dt = x$ for all $x \geq 0$ added 9 characters in body; edited title Apr22 revised Dirac delta question from “Classical covariant fields” by Burgess MathJaxified equations Apr22 revised $x \perp y$ if and only if $\Vert x + \alpha y \Vert \ge \Vert x \Vert$ for all scalars $\alpha$ more descriptive title